An ink cartridge structure for a conventional ink-jet printing apparatus, as disclosed in U.S. Pat. No. 5,409,134, provides a fluid pressure regulating element in the ink reservoir for controlling the back pressure within an operating range that is suitable for preventing ink leakage while permitting the ejecting device to eject ink drops during printing. As shown in this prior patent, the fluid pressure regulation in the rigid ink reservoir can be controlled by flexible bags that are mounted to a curved spring. The pressure within the rigid ink reservoir drops instantly as the ink is ejected from the rigid ink reservoir via the ejecting device. At this moment, the atmosphere pressure is larger than the pressure within the rigid ink reservoir. Thus, ambient air will flow into the flexible bag so that the ink can be ejected smoothly while printing. Moreover, the expansion of the bag causes the deflection of the adjacent springs and thus decreases the ink pressure in the ink reservoir so that the zero ink leakage effect during printing can be achieved.
In another ink cartridge for an ink-jet printing apparatus, for example, the ink cartridge disclosed in U.S. Pat. No. 5,767,882, in order to avoid ink leakage in the process of ink-jet printing, a pressure regulating element is usually provided in the ink reservoir for keeping the pressure within the ink reservoir at a negative pressure so that there is no ink leakage in the printing process.
However, in both of these prior art ink-jet cartridges, a pressure regulating means has to be provided in the ink-jet cartridge and this causes the complexity in structure and assembly of the ink-jet cartridge.